PSA blood tests for prostate cancer should start earlier in life

A study has found that measuring prostate specific antigen (PSA) in the blood may be the best way of identifying men with life-threatening prostate cancer.

The PSA test is used to screen for prostate cancer, but results often lead to an over diagnosis and cancers are treated that would never have become life threatening.

Researchers have been looking at ways to improve the test and thus avoid unnecessary treatment.

Other studies have suggested that PSA velocity, the rate that PSA increases or decreases, is higher in men with life threatening prostate cancer than men without the disease.

This latest study adds supports to the argument that men should have their PSA levels tested when they are young, so doctors have a "baseline" for studying future changes.

Dr. H. Ballentine Carter and colleagues at the Johns Hopkins School of Medicine in Baltimore, assessed the PSA velocity in men who took part in the Baltimore Longitudinal Study of Aging.

Of the men 104 had been diagnosed with prostate cancer but had not died from the disease, 20 men died of prostate cancer, and 856 were without prostate cancer.

Dr. Carter says they found that the rate at which a man's PSA rises may be more important than any absolute level for identifying men who will develop life-threatening cancer while their disease is still curable.

Dr. Carter also says the PSA velocity could be a useful method for identifying those men with a prostate cancer that could be safely monitored in an approach labeled 'active surveillance.'"

PSA is a protein made only by prostate cells, and in cancer, PSA levels can rise as tumour cells multiply, but they also rise as a man's prostate gland grows with age, and some men with cancer have low PSA levels; so the test is considered imperfect.

The authors found that a patient's PSA velocity 10-15 years before their cancer diagnosis, was associated with survival 25 years later and patients with a lower PSA velocity had a 92% survival rate, while patients with a higher PSA velocity had a 54% survival rate.

Men with a higher PSA velocity also had a higher relative risk of death from prostate cancer (1,240 per 100,000 person-years), than men with a low PSA velocity (140 per 100,000 person-years).

Prostate cancer is common and according to the American Cancer Society, this year, 234,460 men in the United States will be diagnosed with the disease, but because the tumours can be very slow-growing only about 30,000 will die of it.

The authors say their data provides a case for PSA testing to begin relatively early in life, when PSA levels are usually lower and prostate enlargement is absent.

This would establish a baseline for evaluating future changes in PSA levels says Carter.

The study is published in the Journal of the National Cancer Institute.